In this paper we evaluate the effect of the acidity of the support (HZSM-5) and the nature of the interaction between the active phases of the bifunctional Pt/HZSM-5 catalyst on the aromatic ring-opening of pyrolysis gasoline under hydrocracking conditions. The catalysts were characterized by N2 adsorption-desorption isotherms, CO chemisorption, pyridine FTIR, NH3 adsorption-DSC and NH3 TPD. The catalyst screening in the pyrolysis gasoline hydrocracking demonstrated that: (i) the conversion of pyrolysis gasoline is linearly dependent on support acidity. At low acidities values the main mechanisms of ring-opening is through hydrogenolysis and thus, the less acidic catalyst shows higher conversion than expected; (ii) the synergysm between the metal and acid-sites is enhanced when using a bifunctional catalyst instead of a hybrid one, due to the increase in H2 spill-over efficiency. However, in terms of activity, the most acid catalyst (hybrid) shows the highest aromatic conversion, in correspondence with (i). © 2008 Elsevier B.V. All rights reserved.